Eucalyptus organosolv lignins: study of the hydroxymethylation and use in resols

Abstract

Lignins obtained from Acetosolv and Formacell delignification of Eucalyptus grandis chips (EAc and EFo, respectively) were reacted with formaldehyde in alkaline medium. The hydroxymethylation was followed by dynamic DSC, to determine the relative reactivity of both lignins. TGA results showed that hydroxymethylated lignins are thermally stable up to 250°C, while the original lignins are stable until 200°C. The synthesis of resols containing EAc and EFo lignins were carried out following multivariate factorial designs (2⁴⁻¹). The effects of four parameters were studied on the synthesis time and on the final viscosity (η). The NaOH:phenolics ratio and the solid content have the more significant effects on the synthesis time and η, for both lignins. Shorter synthesis time is obtained increasing the lignin:phenol ratio from 2:3 to 1:1 for EAc and EFo lignin, but the effect of the HCHO:phenolics ratio is important only for resols containing EFo. For this study, the multivariate experimental design is more adequate than an univariate method, since there is a large interaction between the synthesis parameters as demonstrated by the second order effects.